Wave-Based Patient Line Blockage Detection

ABSTRACT

A dialysis machine (e.g., a peritoneal dialysis (PD) machine) can include a pressure sensor mounted at a proximal end of a patient line that provides PD solution to a patient through a catheter. During treatment, an occlusion can occur at different locations in the patient line and/or the catheter. Elastic waves may be generated at a pump that introduces (e.g., for fill cycles) or withdraws (e.g., for drain cycles) the solution into/out of the patient line. For example, when the solution is introduced or withdrawn suddenly, elastic waves travel distally down the patient line until they encounter the occlusion, and are then reflected back (e.g., toward the pressure sensor).

TECHNICAL FIELD

This disclosure relates to detecting a blockage in a patient line.

BACKGROUND

Dialysis is a treatment used to support a patient with insufficientrenal function. The two principal dialysis methods are hemodialysis andperitoneal dialysis. During hemodialysis (“HD”), the patient's blood ispassed through a dialyzer of a dialysis machine while also passing adialysis solution or dialysate through the dialyzer. A semi-permeablemembrane in the dialyzer separates the blood from the dialysate withinthe dialyzer and allows diffusion and osmosis exchanges to take placebetween the dialysate and the blood stream. These exchanges across themembrane result in the removal of waste products, including solutes likeurea and creatinine, from the blood. These exchanges also regulate thelevels of other substances, such as sodium and water, in the blood. Inthis way, the dialysis machine acts as an artificial kidney forcleansing the blood.

During peritoneal dialysis (“PD”), the patient's peritoneal cavity isperiodically infused with dialysate. The membranous lining of thepatient's peritoneum acts as a natural semi-permeable membrane thatallows diffusion and osmosis exchanges to take place between thesolution and the blood stream. These exchanges across the patient'speritoneum result in the removal of waste products, including soluteslike urea and creatinine, from the blood, and regulate the levels ofother substances, such as sodium and water, in the blood.

Automated PD machines called PD cyclers are designed to control theentire PD process so that it can be performed at home usually overnightwithout clinical staff in attendance. This process is termed continuouscycler-assisted PD (CCPD). Many PD cyclers are designed to automaticallyinfuse, dwell, and drain dialysate to and from the patient's peritonealcavity. The treatment typically lasts for several hours, often beginningwith an initial drain cycle to empty the peritoneal cavity of used orspent dialysate. The sequence then proceeds through the succession offill, dwell, and drain phases that follow one after the other. Eachphase is called a cycle.

SUMMARY

In one aspect, a method includes measuring a first pressure at aproximal end of a medical tube connected to a medical device. The methodalso includes measuring a second pressure at the proximal end of themedical tube. The method also includes determining an elapsed timebetween the first pressure measurement and the second pressuremeasurement. The method also includes determining a location of anocclusion in the medical tube based on the elapsed time.

Implementations can include one or more of the following features.

In some implementations, the medical device includes a dialysis machine.

In some implementations, the dialysis machine includes a peritonealdialysis (PD) machine.

In some implementations, at least one of the first pressure and thesecond pressure includes a local extremum of pressure measurements atthe proximal end of the medical tube.

In some implementations, the local extremum includes at least one of alocal maximum and a local minimum.

In some implementations, the first pressure and the second pressure aremeasured by a pressure sensor mounted at the proximal end of the medicaltube.

In some implementations, the elapsed time represents a period ofoscillations of an elastic wave.

In some implementations, the elastic wave originates from the proximalend of the medical tube.

In some implementations, the elastic wave is generated in response to atleast one of an increase and a decrease in pressure in the medical tube.

In some implementations, a fluid flowing through the medical tube is atleast partially blocked by the occlusion.

In some implementations, the fluid being at least partially blocked bythe occlusion causes an increase or a decrease in pressure in themedical tube.

In some implementations, the at least one of an increase and a decreasein pressure is in response to a motion of a pump of the medical device.

In some implementations, the oscillations of the elastic wave are causedat least in part by the elastic wave being reflected back from thelocation of the occlusion.

In some implementations, the medical tube includes a catheter at adistal end of the medical tube.

In some implementations, the method also includes inferring a type ofthe occlusion based at least in part on the determined location of theocclusion.

In some implementations, the type of the occlusion includes one or moreof a pinch of the medical tube, a kink in the medical tube, a deposit inthe medical tube, and a deposit blocking a hole of a catheter at adistal end of the medical tube.

In some implementations, the deposit includes omental fat.

In some implementations, the method also includes determining thelocation of the occlusion in the medical tube based on the elapsed timeand a wave speed of the elastic wave.

In some implementations, the wave speed of the elastic wave is based onone or more of dimensions of the medical tube, a material composition ofthe medical tube, and a density of a fluid flowing through the medicaltube.

In some implementations, the wave speed of the elastic wave isempirically determined.

In some implementations, the method also includes performing acalibration prior to determining the location of the occlusion. Thecalibration is for determining a wave speed of an elastic wavepropagating through the medical tube.

In some implementations, the calibration is for determining the wavespeed of the elastic wave propagating through the medical tube for aparticular medical tube and cassette configuration used in the medicaldevice.

In another aspect, a method includes measuring a plurality of pressuresat a proximal end of a medical tube connected to a medical device. Themethod also includes determining one or more elapsed times between localextrema of the measured pressures. The method also includes determininga location of an occlusion in the medical tube based on the one or moreelapsed times.

Implementations can include one or more of the following features.

In some implementations, the local extrema include at least one of alocal maximum and a local minimum.

In some implementations, the method also includes removing noisecomponents from the measured pressures before determining the localextrema of the measured pressures.

In some implementations, the magnitudes of the pressure measurementsdecay over time when the occlusion is a partial occlusion.

In some implementations, the method also includes subtracting, from themeasured pressures, values that approximate the decay of the pressuremeasurements as a result of the occlusion being a partial occlusionbefore determining the local extrema.

In some implementations, at least one of the local extrema of themeasured pressures corresponds to an end of a pump motion that causesfluid to flow through the medical tube.

In some implementations, the method also includes determining an elapsedtime between i) the end of the pump motion, and ii) an occurrence of alocal extrema that occurs after the end of the pump motion. The methodalso includes determining the location of the occlusion based on theelapsed time.

In some implementations, the elapsed time represents a first half-waveperiod of oscillations of an elastic wave generated in response to atleast one of an increase and a decrease in pressure in the medical tube.

In some implementations, the method also includes performing one or moresignal processing techniques on the measured pressures.

In another aspect, a method includes measuring a first pressure at aproximal end of a medical tube connected to a medical device. Themedical tube includes a plurality of zones. The method also includesmeasuring a second pressure at the proximal end of the medical tube. Themethod also includes determining an elapsed time between the firstpressure measurement and the second pressure measurement. The methodalso includes determining in which of the plurality of zones anocclusion is located based on the elapsed time.

Implementations can include one or more of the following features.

In some implementations, the medical tube includes five zones.

In some implementations, the medical tube includes a catheter at adistal end of the medical tube. At least one of the zones includes thecatheter.

In some implementations, the medical tube includes a port connecting thecatheter to the medical tube. At least one of the zones includes theport.

In another aspect, a medical device includes a medical tube having aproximal end connected to an outlet of the medical device. The medicaldevice also includes a pressure sensor mounted at the proximal end ofthe medical tube. The pressure sensor is configured for measuring afirst and second pressure at the proximal end of the medical tube. Themedical device also includes a processor configured for determining anelapsed time between the first pressure measurement and the secondpressure measurement. The processor is also configured for determining alocation of an occlusion in the medical tube based on the elapsed time.

Implementations can include one or more of the following features.

In some implementations, the medical device includes a dialysis machine.

In some implementations, the medical device includes a peritonealdialysis machine.

Implementations can include one or more of the following advantages.

In some implementations, the systems and techniques described herein canbe used to determine a location of an occlusion in the medical tube(e.g., in a patient line or in the catheter). In some examples, the typeof occlusion can be inferred based on the determined location. Thedialysis machine can determine an appropriate response for addressingthe particular type of occlusion, including emitting an alert indicatingthe presence of the occlusion and/or adjusting one or more operatingparameters of the dialysis machine in an attempt to clear the occlusionand/or to modulate the flow in the medical tube to avoid an overpressurecondition.

In some implementations, the use of elastic waves for determining thelocation of the occlusion allows the methods described herein to beinsensitive to hydrostatic effects (e.g., which would have a greatereffect on methods that are based on pressure-flow relationships in thefluid).

In some implementations, the dialysis machine is configured to determinethe location of the occlusion using the pressure sensor built into thedialysis machine without requiring a separate pressure sensor.

Other aspects, features, and advantages of the invention will beapparent from the description and drawings, and from the claims.

DESCRIPTION OF DRAWINGS

FIG. 1 shows an example of a peritoneal dialysis (PD) system.

FIG. 2 is a perspective view of a PD cycler and a PD cassette of the PDsystem of FIG. 1, with a door of the PD cycler in the open position toshow the inner surfaces of the PD cycler that interface with the PDcassette during use.

FIG. 3 is a perspective view of an open cassette compartment of the PDcycler of FIG. 1.

FIG. 4 is an exploded, perspective view of the PD cassette of FIG. 2,which includes dome-shaped fastening members that can be mechanicallyconnected to piston heads of the PD cycler of FIG. 1.

FIG. 5 is a perspective, cross-sectional view of the fully assembled PDcassette of FIG. 4.

FIG. 6 is a perspective view of the fully assembled PD cassette of FIG.4, from a flexible membrane and dome-shaped fastening member side of thePD cassette.

FIG. 7 is a perspective view of the fully assembled PD cassette of FIG.4, from a rigid base side of the PD cassette.

FIG. 8 is a perspective view of the PD cassette in the cassettecompartment of the PD cycler of the PD system of FIG. 1.

FIGS. 9A-9G are diagrammatic cross-sectional views of the PD system ofFIG. 1 with the PD cassette disposed in the cassette compartment of thePD cycler, during different phases of a PD treatment and setup.

FIG. 10 shows a schematic diagram of the PD cycler of FIG. 1 connectedto a patient.

FIG. 11 shows an example experimental system for determining apropagation speed of elastic waves.

FIGS. 12A-G show representative graphs of pressures over time asmeasured by a pressure sensor of the system of FIG. 11.

FIG. 13 shows a representative graph of oscillation periods versusvarious clamping distances measured using the experimental system ofFIG. 11.

FIG. 14 shows a schematic of a dialysis system that includes a PDmachine.

FIG. 15 shows a cross-sectional view of an example partial internalocclusion.

FIGS. 16A-B show a cutaway view and a photograph, respectively, of anexample partial external occlusion.

FIG. 17A shows a pressure waveform that includes pressure measurementsover time made by a pressure sensor of the PD machine of FIG. 14.

FIG. 17B shows a pressure waveform that includes a processed version ofthe data of FIG. 17A.

FIG. 18 shows a representative graph of first half-wave periods ofelastic wave oscillations.

FIG. 19 shows a representative graph of second half-wave periods ofelastic wave oscillations.

FIG. 20 shows a representative graph of third half-wave periods ofelastic wave oscillations.

FIG. 21 shows a pressure waveform that includes pressure measurementsover time while performing multiple short-stroke tests.

FIG. 22 shows a computer system and related components.

Like reference symbols in the various drawings indicate like elements.

DETAILED DESCRIPTION

A dialysis machine (e.g., a peritoneal dialysis (PD) machine) caninclude a pressure sensor mounted at a proximal end of a patient linethat provides PD solution to a patient through a catheter. Duringtreatment, an occlusion (e.g., a partial occlusion or a completeocclusion) can occur at different locations in the patient line and/orthe catheter. Elastic waves may be generated at a pump that introduces(e.g., for fill cycles) or withdraws (e.g., for drain cycles) thesolution into/out of the patient line. For example, when the solution isintroduced or withdrawn suddenly, elastic waves travel distally down thepatient line until they encounter the occlusion, and are then reflectedback (e.g., toward the pressure sensor). Utilizing principles of elasticwave theory, the location of the occlusion relative to the pressuresensor can be determined. For example, if the speed and the transit timeof the wave are known, the distance that the wave traveled can bedetermined.

For a patient line of uniform properties, outgoing and reflected waveswill travel at a common speed. This speed can be analytically predictedif the elastic properties and cross-sectional dimensions of the tubingare known, as well as determined based on empirical data. The transittime of the wave can be determined based on elapsed times between localextrema (e.g., local maxima or minima) of pressure measurements made bythe pressure sensor. For example, oscillations in the measured pressurevalues as a result of the waves being reflected can be determined, and aperiod of such oscillations can be measured. The period (e.g., thetransit time of the wave) can be multiplied by the speed of the wave todetermine the distance traveled (e.g., from the pressure sensor, to theocclusion, and back to the pressure sensor), and the distance can bedivided by two to determine the location of the occlusion relative tothe location of the pressure sensor. Because some types of occlusionstypically occur in certain parts of the patient line, the occlusion typecan often be inferred based on the determined location.

The use of elastic waves for determining the location of the occlusionallows the methods described herein to be insensitive to hydrostaticeffects, which would have a greater effect on methods that are based onpressure-flow relationships in the fluid. Further, the methods describedherein operate in the frequency domain. Thus, provided that waves havesufficient amplitude for accurate detection, the results are relativelyinsensitive to amplitude-attenuating effects that may vary from case tocase.

FIG. 1 shows a PD system 100 that includes a PD machine (also generallyreferred to as a PD cycler) 102 seated on a cart 104. Referring also toFIG. 2, the PD machine 102 includes a housing 106, a door 108, and acassette interface 110 that contacts a disposable PD cassette 112 whenthe cassette 112 is disposed within a cassette compartment 114 formedbetween the cassette interface 110 and the closed door 108. A heatertray 116 is positioned on top of the housing 106. The heater tray 116 issized and shaped to accommodate a bag of PD solution such as dialysate(e.g., a 5 liter bag of dialysate). The PD machine 102 also includes auser interface such as a touch screen display 118 and additional controlbuttons 120 that can be operated by a user (e.g., a caregiver or apatient) to allow, for example, set up, initiation, and/or terminationof a PD treatment.

Dialysate bags 122 are suspended from fingers on the sides of the cart104, and a heater bag 124 is positioned in the heater tray 116. Thedialysate bags 122 and the heater bag 124 are connected to the cassette112 via dialysate bag lines 126 and a heater bag line 128, respectively.The dialysate bag lines 126 can be used to pass dialysate from dialysatebags 122 to the cassette 112 during use, and the heater bag line 128 canbe used to pass dialysate back and forth between the cassette 112 andthe heater bag 124 during use. In addition, a patient line 130 and adrain line 132 are connected to the cassette 112. The patient line 130can be connected to a patient's abdomen via a catheter (e.g., thecatheter 1002 of FIG. 10) and can be used to pass dialysate back andforth between the cassette 112 and the patient's peritoneal cavityduring use. The catheter 1002 may be connected to the patient line 130via a port (1004 of FIG. 10) such as a fitting. The drain line 132 canbe connected to a drain or drain receptacle and can be used to passdialysate from the cassette 112 to the drain or drain receptacle duringuse.

The PD machine 102 also includes a control unit 139 (e.g., a processor).The control unit 139 can receive signals from and transmit signals tothe touch screen display 118, the control panel 120, and the variousother components of the PD system 100. The control unit 139 can controlthe operating parameters of the PD machine 102. In some implementations,the control unit 139 is an MPC823 PowerPC device manufactured byMotorola, Inc.

FIG. 3 shows a more detailed view of the cassette interface 110 and thedoor 108 of the PD machine 102. As shown, the PD machine 102 includespistons 133A, 133B with piston heads 134A, 134B attached to pistonshafts 135A, 135B (piston shaft 135A shown in FIGS. 9A-G) that can beaxially moved within piston access ports 136A, 136B formed in thecassette interface 110. The pistons 133A, 133B, piston heads 134A, 134B,and piston shafts 135A, 135B are sometimes referred to herein as pumps.The piston shafts 135A, 135B are connected to stepper motors that can beoperated to move the pistons 133A, 133B axially inward and outward suchthat the piston heads 134A, 134B move axially inward and outward withinthe piston access ports 136A, 136B. The stepper motors drive leadscrews, which move nuts inward and outward along the lead screws. Thestepper motors may be controlled by driver modules (e.g., the drivermodules 1438 a, 1438 b of FIG. 14). The nuts, in turn, are connected tothe pistons 133A, 133B and thus cause the pistons 133A, 133B to moveinward and outward as the stepper motors rotate the lead screws. Steppermotor controllers (e.g., in communication with the microcontroller 1436of FIG. 14) provide the necessary current to be driven through thewindings of the stepper motors to move the pistons 133A, 133B. Thepolarity and sequencing of the current determines whether the pistons133A, 133B are advanced or retracted. In some implementations, thestepper motors require 200 steps to make a full rotation, and thiscorresponds to 0.048 inch of linear travel (e.g., for a leadscrew with agiven thread pitch).

The PD system 100 also includes encoders (e.g., optical encoders) thatmeasure the rotational movement of the lead screws. The axial positionsof the pistons 133A, 133B can be determined based on the rotationalmovement of the lead screws, as determined by the encoders. Thus, themeasurements of the encoders can be used to accurately position thepiston heads 134A, 134B of the pistons 133A, 133B.

As discussed below, when the cassette 112 (shown in FIGS. 2 and 4-7) ispositioned within the cassette compartment 114 of the PD machine 102with the door 108 closed, the piston heads 134A, 134B of the PD machine102 align with pump chambers 138A, 138B of the cassette 112 such thatthe piston heads 134A, 134B can be mechanically connected to dome-shapedfastening members 161A, 161B of the cassette 112 overlying the pumpchambers 138A, 138B. As a result of this arrangement, movement of thepiston heads 134A, 134B toward the cassette 112 during treatment candecrease the volume of the pump chambers 138A, 138B and force dialysateout of the pump chambers 138A, 138B, while retraction of the pistonheads 134A, 134B away from the cassette 112 can increase the volume ofthe pump chambers 138A, 138B and cause dialysate to be drawn into thepump chambers 138A, 138B.

As shown in FIG. 3, the cassette interface 110 includes two pressuresensors 151A, 151B that align with pressure sensing chambers 163A, 163B(shown in FIGS. 2, 4, 6, and 7) of the cassette 112 when the cassette112 is positioned within the cassette compartment 114. Portions of amembrane 140 of the cassette 112 that overlie the pressure sensingchambers 163A, 163B adhere to the pressure sensors 151A, 151B usingvacuum pressure. Specifically, clearance around the pressure sensors151A, 151B communicates vacuum to the portions of the cassette membrane140 overlying the pressure sensing chambers 163A, 163B to hold thoseportions of the cassette membrane 140 tightly against the pressuresensors 151A, 151B. The pressure of fluid within the pressure sensingchambers 163A, 163B causes the portions of the cassette membrane 140overlying the pressure sensing chambers 163A, 163B to contact and applypressure to the pressure sensors 151A, 151B.

The pressure sensors 151A, 151B can be any sensors that are capable ofmeasuring the fluid pressure in the sensing chambers 163A, 163B. In someimplementations, the pressure sensors are solid state silicon diaphragminfusion pump force/pressure transducers. One example of such a sensoris the Model 1865 force/pressure transducer manufactured by SensymFoxboro ICT. In some implementations, the force/pressure transducer ismodified to provide increased voltage output. The force/pressuretransducer can, for example, be modified to produce an output signal of0 to 5 volts.

Still referring to FIG. 3, the PD machine 102 also includes multipleinflatable members 142 positioned within inflatable member ports 144 inthe cassette interface 110. The inflatable members 142 align withdepressible dome regions 146 of the cassette 112 (shown in FIGS. 4-6)when the cassette 112 is positioned within the cassette compartment 114of the PD machine 102. While only a couple of the inflatable members 142are labeled in FIG. 3, it should be understood that the PD machine 102includes an inflatable member 142 associated with each of thedepressible dome regions 146 of the cassette 112. The inflatable members142 act as valves to direct dialysate through the cassette 112 in adesired manner during use. In particular, the inflatable members 142bulge outward beyond the surface of the cassette interface 110 and intocontact with the depressible dome regions 146 of the cassette 112 wheninflated, and retract into the inflatable member ports 144 and out ofcontact with the cassette 112 when deflated. By inflating certaininflatable members 142 to depress their associated dome regions 146 onthe cassette 112, certain fluid flow paths within the cassette 112 canbe occluded. Thus, dialysate can be pumped through the cassette 112 byactuating the piston heads 134A, 134B, and can be guided along desiredflow paths within the cassette 112 by selectively inflating anddeflating the various inflatable members 142.

Still referring to FIG. 3, locating pins 148 extend from the cassetteinterface 110 of the PD machine 102. When the door 108 is in the openposition, the cassette 112 can be loaded onto the cassette interface 110by positioning the top portion of the cassette 112 under the locatingpins 148 and pushing the bottom portion of the cassette 112 toward thecassette interface 110. The cassette 112 is dimensioned to remainsecurely positioned between the locating pins 148 and a spring loadedlatch 150 extending from the cassette interface 110 to allow the door108 to be closed over the cassette 112. The locating pins 148 help toensure that proper alignment of the cassette 112 within the cassettecompartment 114 is maintained during use.

The door 108 of the PD machine 102, as shown in FIG. 3, definescylindrical recesses 152A, 152B that substantially align with thepistons 133A, 133B when the door 108 is in the closed position. When thecassette 112 (shown in FIGS. 4-7) is positioned within the cassettecompartment 114, hollow projections 154A, 154B of the cassette 112,inner surfaces of which partially define the pump chambers 138A, 138B,fit within the recesses 152A, 152B. The door 108 further includes a padthat is inflated during use to compress the cassette 112 between thedoor 108 and the cassette interface 110. With the pad inflated, theportions of the door 108 forming the recesses 152A, 152B support theprojections 154A, 154B of the cassette 112 and the planar surface of thedoor 108 supports the other regions of the cassette 112. The door 108can counteract the forces applied by the inflatable members 142 and thusallows the inflatable members 142 to actuate the depressible domeregions 146 on the cassette 112. The engagement between the door 108 andthe hollow projections 154A, 154B of the cassette 112 can also help tohold the cassette 112 in a desired fixed position within the cassettecompartment 114 to further ensure that the pistons 133A, 133B align withthe fluid pump chambers 138A, 138B of the cassette 112.

The control unit (139 of FIG. 1) is connected to the pressure sensors151A, 151B, to the stepper motors (e.g., the drivers of the steppermotors) that drive the pistons 133A, 133B, and to the encoders thatmonitor rotation of the lead screws of the stepper motors such that thecontrol unit 139 can receive signals from and transmit signals to thosecomponents of the system. The control unit 139 monitors the componentsto which it is connected to determine whether any complications existwithin the PD system 100, such as the presence of an occlusion.

FIG. 4 is an exploded, perspective view of the cassette 112, FIG. 5 is aperspective, cross-sectional view of the fully assembled cassette 112,and FIGS. 6 and 7 are perspective views of the assembled cassette 112,from the membrane side and from the rigid base side, respectively.Referring to FIGS. 4-6, the flexible membrane 140 of the cassette 112 isattached to a periphery of the tray-like rigid base 156. Rigiddome-shaped fastening members 161A, 161B are positioned within recessedregions 162A, 162B of the base 156. The dome-shaped fastening members161A, 161B are sized and shaped to receive the piston heads 134A, 134Bof the PD machine 102 of FIG. 3. In some implementations, thedome-shaped fastening members 161A, 161B have a diameter, measured fromthe outer edges of flanges 164A, 164B, of about 1.5 inches to about 2.5inches (e.g., about 2.0 inches) and take up about two-thirds to aboutthree-fourths of the area of the recessed regions 162A, 162B. Theannular flanges 164A, 164B of the rigid dome-shaped fastening members161A, 161B are attached in a liquid-tight manner to portions of theinner surface of the membrane 140 surrounding substantially circularapertures 166A, 166B formed in the membrane 140. The annular flanges164A, 164B of the rigid dome-shaped fastening members 161A, 161B can,for example, be thermally bonded or adhesively bonded to the membrane140. The apertures 166A, 166B of the membrane 140 expose the rigiddome-shaped fastening members 161A, 161B such that the piston heads134A, 134B are able to directly contact and mechanically connect to thedome-shaped fastening members 161A, 161B during use.

The annular flanges 164A, 164B of the dome-shaped fastening members161A, 161B, as shown in FIG. 5, form annular projections 168A, 168B thatextend radially inward and annular projections 176A, 176B that extendradially outward from the side walls of the dome-shaped fasteningmembers 161A, 161B. When the piston heads 134A, 134B (shown in FIG. 3)are mechanically connected to the dome-shaped fastening members 161A,161B, the radially inward projections 168A, 168B engage the rear angledsurfaces of the sliding latches 145A, 147A of the piston heads 134A,134B to firmly secure the dome-shaped fastening members 161A, 161B tothe piston heads 134A, 134B. Because the membrane 140 is attached to thedome-shaped fastening members 161A, 161B, movement of the dome-shapedfastening members 161A, 161B into and out of the recessed regions 162A,162B of the base 156 (e.g., due to reciprocating motion of the pistons133A, 133B of FIG. 3) causes the flexible membrane 140 to similarly bemoved into and out of the recessed regions 162A, 162B of the base 156.This movement allows fluid to be forced out of and drawn into the fluidpump chambers 138A, 138B, which are formed between the recessed regions162A, 162B of the base 156 and the portions of the dome-shaped fasteningmembers 161A, 161B and membrane 140 that overlie those recessed regions162A, 162B.

Referring to FIGS. 4 and 6, raised ridges 167 extend from thesubstantially planar surface of the base 156 towards and into contactwith the inner surface of the flexible membrane 140 when the cassette112 is compressed between the door 108 and the cassette interface 110 ofthe PD machine 102 to form a series of fluid passageways 158 and to formthe multiple, depressible dome regions 146, which are widened portions(e.g., substantially circular widened portions) of the fluid pathways158, as shown in FIG. 6. The fluid passageways 158 fluidly connect thefluid line connectors 160 of the cassette 112, which act as inlet/outletports of the cassette 112, to the fluid pump chambers 138A, 138B. Asnoted above, the various inflatable valve members 142 of the PD machine102 act on the cassette 112 during use. During use, the dialysate flowsto and from the pump chambers 138A, 138B through the fluid pathways 158and dome regions 146. At each depressible dome region 146, the membrane140 can be deflected to contact the planar surface of the base 156 fromwhich the raised ridges 167 extend. Such contact can substantiallyimpede (e.g., prevent) the flow of dialysate along the region of thepathway 158 associated with that dome region 146. Thus, the flow ofdialysate through the cassette 112 can be controlled through theselective depression of the depressible dome regions 146 by selectivelyinflating the inflatable members 142 of the PD machine 102.

Still referring to FIGS. 4 and 6, the fluid line connectors 160 arepositioned along the bottom edge of the cassette 112. As noted above,the fluid pathways 158 in the cassette 112 lead from the pumpingchambers 138A, 138B to the various connectors 160. The connectors 160are positioned asymmetrically along the width of the cassette 112. Theasymmetrical positioning of the connectors 160 helps to ensure that thecassette 112 will be properly positioned in the cassette compartment 114with the membrane 140 of the cassette 112 facing the cassette interface110. The connectors 160 are configured to receive fittings on the endsof the dialysate bag lines 126, the heater bag line 128, the patientline 130, and the drain line 132. In some examples, the connectors 160are bonded to tubing that is integral cassette 112. One end of thefitting can be inserted into and bonded to its respective line and theother end can be inserted into and bonded to its associated connector160. By permitting the dialysate bag lines 126, the heater bag line 128,the patient line 130, and the drain line 132 to be connected to thecassette, as shown in FIGS. 1 and 2, the connectors 160 allow dialysateto flow into and out of the cassette 112 during use. As the pistons133A, 133B are reciprocated, the inflatable members 142 can beselectively inflated to allow fluid to flow from any of the lines 126,128, 130, and 132 to any of ports 185A, 185B, 187A, and 187B of the pumpchambers 138A, 138B, and vice versa.

The rigidity of the base 156 helps to hold the cassette 112 in placewithin the cassette compartment 114 of the PD machine 102 and to preventthe base 156 from flexing and deforming in response to forces applied tothe projections 154A, 154B by the dome-shaped fastening members 161A,161B and in response to forces applied to the planar surface of the base156 by the inflatable members 142. The dome-shaped fastening members161A, 161B are also sufficiently rigid that they do not deform as aresult of usual pressures that occur in the pump chambers 138A, 138Bduring the fluid pumping process. Thus, the deformation or bulging ofthe annular portions 149A, 149B of the membrane 140 can be assumed to bethe only factor other than the movement of the pistons 133A, 133B thataffects the volume of the pump chambers 138A, 138B during the pumpingprocess.

The base 156 and the dome-shaped fastening members 161A, 161B of thecassette 112 can be formed of any of various relatively rigid materials.In some implementations, these components of the cassette 112 are formedof one or more polymers, such as polypropylene, polyvinyl chloride,polycarbonate, polysulfone, and other medical grade plastic materials.In some implementations, these components can be formed of one or moremetals or alloys, such as stainless steel. These components of canalternatively be formed of various different combinations of theabove-noted polymers and metals. These components of the cassette 112can be formed using any of various different techniques, includingmachining, molding, and casting techniques.

As noted above, the membrane 140 is attached to the periphery of thebase 156 and to the annular flanges 164A, 164B of the dome-shapedfastening members 161A, 161B. The portions of the membrane 140 overlyingthe remaining portions of the base 156 are typically not attached to thebase 156. Rather, these portions of the membrane 140 sit loosely atopthe raised ridges 165A, 165B, and 167 extending from the planar surfaceof the base 156. Any of various attachment techniques, such as adhesivebonding and thermal bonding, can be used to attach the membrane 140 tothe periphery of the base 156 and to the dome-shaped fastening members161A, 161B. The thickness and material(s) of the membrane 140 areselected so that the membrane 140 has sufficient flexibility to flextoward the base 156 in response to the force applied to the membrane 140by the inflatable members 142. In some implementations, the membrane 140is about 100 micron to about 150 micron in thickness. However, variousother thicknesses may be sufficient depending on the type of materialused to form the membrane 140.

As shown in FIG. 8, before treatment, the door 108 of the PD machine 102is opened to expose the cassette interface 110, and the cassette 112 ispositioned with its dome-shaped fastening members 161A, 161B alignedwith the pistons 133A, 133B of the PD machine 102, its pressure sensingchambers 163A, 163B aligned with the pressure sensors 151A, 151B of thePD machine 102, its depressible dome regions 146 aligned with theinflatable members 142 of the PD machine 102, and its membrane 140adjacent to the cassette interface 110. In order to ensure that thecassette 112 is properly positioned on the cassette interface 110, thecassette 112 is positioned between the locating pins 148 and the springloaded latch 150 extending from the cassette interface 110. Theasymmetrically positioned connectors 160 of the cassette act as a keyingfeature that reduces the likelihood that the cassette 112 will beinstalled with the membrane 140 and dome-shaped fastening members 161A,161B facing in the wrong direction (e.g., facing outward toward the door108). Additionally or alternatively, the locating pins 148 can bedimensioned to be less than the maximum protrusion of the projections154A, 154B such that the cassette 112 cannot contact the locating pins148 if the membrane 140 is facing outward toward the door 108. Thepistons 133A, 133B are typically retracted into the piston access ports136A, 136B during installation of the cassette 112 to avoid interferencebetween pistons 133A, 133B and the dome-shaped fastening members 161A,161B and thus increase the ease with which the cassette 112 can bepositioned within the cassette compartment 114.

After positioning the cassette 112 as desired on the cassette interface110, the door 108 is closed and the inflatable pad within the door 108is inflated to compress the cassette 112 between the inflatable pad andthe cassette interface 110. This compression of the cassette 112 holdsthe projections 154A, 154B of the cassette 112 in the recesses 152A,152B of the door 108 and presses the membrane 140 tightly against theraised ridges 167 extending from the planar surface of the rigid base156 to form the enclosed fluid pathways 158 and dome regions 146 (shownin FIG. 6). Referring briefly also to FIGS. 1 and 2, the patient line130 is then connected to a patient's abdomen via a catheter, and thedrain line 132 is connected to a drain or drain receptacle. In addition,the heater bag line 128 is connected to the heater bag 124, and thedialysate bag lines 126 are connected to the dialysate bags 122. At thispoint, the pistons 133A, 133B can be coupled to dome-shaped fasteningmembers 161A, 161B of the cassette 112 to permit priming of the cassette112 and the lines 126, 128, 130, 132. Once these components have beenprimed, treatment can be initiated.

FIGS. 9A-9G, which will be discussed below, are cross-sectional views ofthe system during different stages of the setup, priming, and treatment.These figures focus on the interaction between the piston 133A of the PDmachine 102 and the pump chamber 138A of the cassette 112 during thesetup, priming, and treatment. The interaction between the other piston133B and pump chamber 138B is identical and thus will not be separatelydescribed in detail.

FIG. 9A shows the piston 133A fully retracted into the piston accessport 136A of the cassette interface 110. The cassette 112 is positionedin the cassette compartment 114 of the PD machine 102 and the inflatablepad in the door 108 of the PD machine 102 is inflated such that thecassette 112 is pressed tightly against the cassette interface 110 ofthe PD machine 102, as explained above.

Referring to FIG. 9B, with the cassette 112 properly installed withinthe cassette compartment 114 of the PD machine 102 and the appropriateline connections made, the piston 133A is advanced to initiate theprocess of mechanically connecting the piston head 134A of the PDmachine 102 to the dome-shaped fastening member 161A of the cassette112. As the piston 133A is advanced, a front angled surface 188A of asliding latch 145A and a front angled surface 191A of a sliding latch147A contact a rear surface of the annular projection 168A, whichextends radially inward from the dome-shaped fastening member 161A. Therear surface of the annular projection 168A is approximatelyperpendicular to the longitudinal axis of the piston 133A.

As the piston 133A continues to advance, the dome-shaped fasteningmember 161A contacts the inner surface of the portion of the rigid base156 that forms the recessed region 162A, as shown in FIG. 9B. The rigidbase 156 prevents further forward movement of the dome-shaped fasteningmember 161A. The membrane 140, which is attached to the peripheralflange 164A of the dome-shaped fastening member 161A, also stretches andmoves into the recessed region 162A due to the advancing piston 133A.Due to the angled geometries of the front angled surfaces 188A, 191A ofthe sliding latches 145A, 147A and the resistance provided by the rigidbase 156 to the forward motion of the dome-shaped fastening member 161A,the sliding latches 145A, 147A are caused to move radially inward (i.e.,toward the longitudinal axis of the piston 133A) as the piston head 134Acontinues to be advanced relative to the dome-shaped fastening member161A. More specifically, the forward motion of the sliding latches 145A,147A is converted into a combined forward and radially inward motion dueto the sliding motion of the front angled surfaces 188A, 191A of thesliding latches 145A, 147A against the rear surface of the annularprojection 168A of the dome-shaped fastening member 161A. The radialinward movement of each of the sliding latches 145A, 147A in turn causesa forward movement of a latch lock 141A of the piston head 134A due tothe mated geometries of the outer surfaces of legs 155A, 157A of thelatch lock 141A and the surfaces of the sliding latches 145A, 147A thatare positioned adjacent to and brought into contact with those outersurfaces of the legs 155A, 157A. This forward movement of the latch lock141A is resisted by a spring 143A in the piston head.

FIG. 9C shows the piston head 134A at a point during the connectionprocess at which the sliding latches 145A, 147A have been deflectedradially inward a sufficient distance to allow the sliding latches 145A,147A to pass beyond the annular projection 168A that extends radiallyinward from the dome-shaped fastening member 161A. In this position,outer peripheral surfaces of the sliding latches 145A, 147A, which aresubstantially parallel to the longitudinal axis of the piston 133A,contact and slide along an inner surface of the annular projection 168Aof the dome-shaped fastening member 161A, which is also substantiallyparallel to the longitudinal axis of the piston 133A. The spring 143A isfurther compressed due to the radially inwardly deflected positions ofthe sliding latches 145A, 147A.

Referring to FIG. 9D, as the sliding latches 145A, 147A pass beyond theannular projection 168A, the spring 143A is allowed to expand. Theexpansion of the spring 143A causes the latch lock 141A to moverearward. As a result, the outer surfaces of the legs 155A, 157A of thelatch lock 141A contact the correspondingly angled adjacent surfaces ofthe sliding latches 145A, 147A, causing the sliding latches 145A, 147Ato move radially outward underneath the projection 168A of thedome-shaped fastening member 161A. Rear angled surfaces 190A, 193A ofthe sliding latches 145A, 147A ride along the front surface of theprojection 168A of the dome-shaped fastening member 161A, which isslightly angled toward the rear of the dome-shaped fastening member161A, as the sliding latches 145A, 147A move radially outward. Thesliding latches 145A, 147A become wedged beneath the projection 168A asthe sliding latches 145A, 147A move radially outward.

FIG. 9E illustrates the completed mechanical connection between thepiston head 134A and the dome-shaped fastening member 161A in which thesliding latches 145A, 147A have moved to maximum outwardly displacedpositions within the dome-shaped fastening member 161A. In thisconfiguration, the projection 168A of the dome-shaped fastening member161A is effectively pinched between a rear member 137A of the pistonhead 134A and the sliding latches 145A, 147A, resulting in a secureengagement between the piston head 134A and the dome-shaped fasteningmember 161A. As a result of the secure engagement of the piston head134A to the dome-shaped fastening member 161A, the amount of slippage ofthe piston head 134A relative to the dome-shaped fastening member 161Acan be reduced (e.g., minimized) and thus precise pumping can beachieved.

After mechanically coupling the piston head 134A of the PD machine 102to the dome-shaped fastening member 161A of the cassette 112, a primingtechnique is carried out to remove air from the cassette 112 and fromthe various lines 126, 128, 130, 132 connected to the cassette 112. Toprime the cassette 112 and the lines 126, 128, 130, 132, the piston 133Aand inflatable members 142 are typically operated to pump dialysate fromthe heater bag 124 to the drain and from each of the dialysate bags 122to the drain. Dialysate is also passed (e.g., by gravity) from theheater bag 124 to the patient line 130 to force any air trapped in thepatient line out of a hydrophobic filter positioned at the distal end ofthe patient line 130.

After priming is complete, the patient line 130 is connected to thepatient and the PD machine 102 is operated to drain any spent dialysatethat was left in the patient's peritoneal cavity from a previoustreatment. To drain the spent dialysate from the patient's peritonealcavity, the inflatable members 142 of the PD machine 102 are configuredto create an open fluid flow path between the patient line 130 and theport 187A (shown in FIG. 4) of the pump chamber 138A, and the piston133A is retracted to draw spent dialysate from the peritoneal cavity ofthe patient into the pump chamber 138A via the patient line 130, asshown in FIG. 9F. Because the piston head 134A is mechanically connectedto the dome-shaped fastening member 161A and the dome-shaped fasteningmember 161A is attached to the membrane 140 of the cassette 112, theretraction of the piston 133A causes the dome-shaped fastening member161A and the portion of the membrane 140 attached to the dome-shapedfastening member 161A to move rearwardly. As a result, the volume of thepump chamber 138A is increased and spent dialysate is drawn into thepump chamber 138A from the peritoneal cavity of the patient. The spentdialysate travels from the patient line 130 through the pressure sensingchamber 163A and then enters the pump chamber 138A via the port 187A.The pressure sensor 151A is able to monitor the pressure in the pressuresensing chamber 163A, which is approximately equal to the pressure inthe pump chamber 138A, during this process.

Referring to FIG. 9G, after drawing the dialysate into the pump chamber138A from the peritoneal cavity of the patient, the inflatable members142 are configured to create an open fluid flow path between the port185A (shown in FIG. 4) of the pump chamber 138A and the drain line 132,and the dialysate is forced out of the pump chamber 138A to the drain byadvancing the piston 133A and decreasing the volume of the pump chamber138A. The piston 133A is typically advanced until the dome-shapedfastening member 161A contacts or nearly contacts the inner surface ofthe recessed region of the base 156 so that substantially all of thedialysate is forced out of the fluid pump chamber 138A via the port185A.

During the patient drain phase of the treatment, the pistons 133A, 133Bare typically alternately operated such that the piston 133A isretracted to draw spent dialysate solution into the pump chamber 138Afrom the patient while the piston 133B is advanced to pump spentdialysate solution from the pump chamber 138B to the drain and viceversa.

To begin the patient fill phase, the inflatable members 142 areconfigured to create a fluid flow path between the pump chamber 138A andthe heater bag line 128, and then the piston 133A is retracted, as shownin FIG. 9F, to draw warm dialysate from the heater bag 124 to the pumpchamber 138A. The warm dialysate travels from the heater bag 124 throughthe heater bag line 128 and into the pump chamber via the port 185A.

The warm dialysate is then delivered to the peritoneal cavity of thepatient via the patient line 130 by configuring the inflatable members142 to create a clear fluid flow path between the pump chamber 138A andthe patient line 130 and advancing the piston 133A, as shown in FIG. 9G.The warm dialysate exits the pump chamber 138A via the port 187A andtravels through the pressure sensing chamber 163A to the patient line130 before reaching the peritoneal cavity of the patient. The pressuresensor 151A is able to monitor the pressure in the pressure sensingchamber 163A, which is approximately equal to the pressure in the pumpchamber 138A, during this process.

During the patient fill phase of the treatment, the pistons 133A, 133Bare typically alternately operated such that the piston 133A isretracted to draw warm dialysate into the pump chamber 138A from theheater bag 124 while the piston 133B is advanced to pump warm dialysatefrom the pump chamber 138B to the patient and vice versa. When thedesired volume of dialysate has been pumped to the patient, the machine102 transitions from the patient fill phase to a dwell phase duringwhich the dialysate is allowed to sit within the peritoneal cavity ofthe patient for a long period of time.

During the dwell period, toxins cross the peritoneum of the patient intothe dialysate from the patient's blood. As the dialysate dwells withinthe patient, the PD machine 102 prepares fresh dialysate for delivery tothe patient in a subsequent cycle. In particular, the PD machine 102pumps fresh dialysate from one of the four full dialysate bags 122 intothe heater bag 124 for heating. To do this, the pump of the PD machine102 is activated to cause the pistons 133A, 133B to reciprocate andcertain inflatable members 142 of the PD machine 102 are inflated tocause the dialysate to be drawn into the fluid pump chambers 138A, 138Bof the cassette 112 from the selected dialysate bag 122 via itsassociated line 126. The dialysate is then pumped from the fluid pumpchambers 138A, 138B to the heater bag 124 via the heater bag line 128.

After the dialysate has dwelled within the patient for the desiredperiod of time, the spent dialysate is pumped from the patient to thedrain in the manner described above. The heated dialysate is then pumpedfrom the heater bag 124 to the patient where it dwells for a desiredperiod of time. These steps are repeated with the dialysate from two ofthe three remaining dialysate bags 122. The dialysate from the lastdialysate bag 122 is typically delivered to the patient and left in thepatient until the subsequent PD treatment.

After completion of the PD treatment, the pistons 133A, 133B areretracted in a manner to disconnect the piston heads 134A, 134B from thedome-shaped fastening members 161A, 161B of the cassette. The door 108of the PD machine 102 is then opened and the cassette 112 is removedfrom the cassette compartment 114 and discarded.

FIG. 10 shows a schematic diagram of the PD machine 102 connected to apatient. The patient line 130 is connected to the patient's abdomen viathe catheter 1002, and the catheter is connected to the patient line viathe port 1004. The patient line 130 may be a tube made of a flexiblematerial (e.g., a polymer) that is at least partially distended byoperating pressures in the PD machine 102. For example, the patient line130 may be an elastic polymer tube that develops a swell in response topositive operating pressures in the PD machine 102. The patient line130, the port 1004, and the catheter 1002 are sometimes referred toherein as the patient line-catheter conduit, or simply the conduit. Atleast one of the pressure sensors 151A, 151B is located at a proximalend of the patient line 130 (e.g., at the end of the patient line 130that is nearest to the PD machine 102). At least one of the pressuresensors 151A, 151B is selectably configured to measure the pressure inthe patient line 130. In some implementations, the pressure sensors151A, 151B include a transducer that generates a signal as a function ofthe pressure imposed. The signal is indicative of the magnitude and signof the measured pressure.

During a PD treatment cycle, an occlusion can occur at differentlocations in the conduit. For example, the patient line 130 may becomekinked or pinched, holes in the catheter 1002 may become occluded (e.g.,with omental fat), or the patient line 130 may develop an internalblockage at some location (e.g., from a deposit of omental fat). The PDmachine 102 is configured to adjust its operation in response to anocclusion being detected. For example, the control unit 139 may beconfigured to adjust one or more operating parameters of the PD machine102 in an attempt to clear the occlusion and/or to modulate the flow inthe patient line to avoid an overpressure condition. In someimplementations, the control unit 139 may be configured to provide analert indicating that an occlusion has been detected. For example, avisual, tactile, and/or audible alert may be directed to the patient(e.g., to wake the patient).

In order to determine an appropriate response, the PD machine 102 isconfigured to ascertain the type of occlusion that is present. In someimplementations, the type of occlusion can be inferred based on thelocation of the occlusion in the conduit. For example, if an occlusionis detected in the catheter 1002, the PD machine 102 can infer thatholes in the catheter 1002 may be occluded. Similarly, if the occlusionis detected somewhere along the patient line 130, the PD machine 102 caninfer that the patient line 130 is kinked or pinched. The PD machine 102is configured to determine a location of the occlusion relative to theposition of the pressure sensor 151A, 151B. The particular location ofthe occlusion can be considered by the PD machine 102 to determine theappropriate response. In the example shown in FIG. 10, an occlusion 1008is present in the patient line 130 at a distance x from the pressuresensor 151A (e.g., at or near the patient line inlet), which may beindicative of a kink or a pinch in the patient line 130.

Motion (e.g., rapid motion) of the pump mechanism creates an impulse(e.g., a step input and/or a near-instantaneous pulse) in localpressure. The onset or stoppage of flow of the PD solution (e.g., thedialysate) can present a wavefront. In response, the patient line 130may develop a deformity. For example, the elastic material of thepatient line 130 may locally expand (in the case of positive pressure)or locally contract (in the case of negative pressure) in response tothe step input. The local (e.g., positive or negative) distension incross-sectional area travels axially along the wall of the patient line130 itself (e.g., as opposed to traveling in the PD solution) as anelastic wave. The wave carries with it local pressure variations, whichmay be detected by the pressure sensor 151A, 151B that is sampling fastenough to resolve the pulse as it travels.

When an elastic wave encounter a discontinuity in the dispersionrelation of the elastic wave, at least a portion of the wave isreflected back toward the source. An occlusion in the conduit, or a kinkor pinch in the line, are examples of such a discontinuity. Thus, whenthe elastic wave encounters the occlusion 1008, at least a portion isreflected back toward the pressure sensor 151A, 151B. The speed at whichthe elastic wave travels (e.g., the propagation speed) is the same inboth directions, and is a function of the material properties and thegeometry (e.g., cross-sectional geometry) of the materials comprisingthe conduit. The pressure sensor 151A, 151B is used to determine thetiming of the wave's motion. For example, a single pulse can be detectedas a difference in timing, and a period of an oscillatory wave can bemeasured.

If the propagation speed c_(o) of the elastic wave is known, and thetime required for the elastic wave to travel from the pressure sensor151A, to the occlusion 1008, and back to the pressure sensor 151A Tisknown, the distance traveled by the elastic waves (e.g., from thepressure sensor 151A, to the occlusion 1008, and back to the pressuresensor 151A) can be determined. The distance traveled can be divided bytwo to determine the location of the occlusion 1008 in the conduitrelative to the location of the pressure sensor 151A. That is, thedistance x along the conduit from the location of the pressure sensor151A to the location of the occlusion 1008 can be determined accordingto Equation 1:

$\begin{matrix}{x = \frac{T*c_{o}}{2}} & (1)\end{matrix}$

where T is the transit time of the elastic waves, c_(o) is thepropagation speed of the elastic waves, and x is the distance along theconduit from the location of the pressure sensor 151A to the location ofthe occlusion 1008 for the first reflection of the wave. The wavereflections continue; the reflected wave is again reflected by theproximal end of the tube, the reflection travels back toward theocclusion, and is in turn reflected back. At each step, energy is lost,thereby resulting in an oscillation with a decaying amplitude.

The propagation speed c_(o) of the elastic wave in distensible tubingcarrying an incompressible fluid can be determined according to Equation2:

$\begin{matrix}{c_{o} = {\frac{A}{\rho}\sqrt{\frac{\partial P}{\partial A}}}} & (2)\end{matrix}$

where A is the cross-sectional area of the lumen of the tubing, ρ is thedensity of the fluid, and P is the local transmural pressure. The valueof the term

$\frac{\partial P}{\partial A}$

comes from the stress-strain relationship of the tubing. Thus, this termis a function of the elastic modulus of the tubing material and of thetube's cross-sectional dimensions. Accordingly, Equation 2 confirms thatthe propagation speed c_(o) is a function of the material properties ofthe tube, the dimensions of the tube, and the density of the fluidtraveling through the tube.

As mentioned above, elastic waves can be reflected (or, e.g., scattered)when they reach a discontinuity in the carrying medium. In the case ofthe 1-dimensional waves of interest in this example, such adiscontinuity may be represented by a change in the characteristicimpedance Z_(o) of the tubing. The characteristic impedance Z_(o) for aharmonic forcing of pressure waves (e.g., at frequency ω) in such atube, accounting for the effect of viscous damping, can be determinedaccording to Equation 3:

$\begin{matrix}{Z_{o} = {\frac{\rho \; c_{o}^{2}}{i\; \omega \; A_{o}}\lambda}} & (3)\end{matrix}$

where A_(o) is the luminal area at zero P, i represents the imaginarynumber √{square root over (−1)}, and λ is given by Equation 4:

$\begin{matrix}{\lambda = \left\lbrack {\frac{1}{\rho \; c_{o}^{2}}\left( {{- {\rho\omega}^{2}} + \frac{8{\pi\mu}\; i\; \omega}{A_{o}}} \right)} \right\rbrack^{1/2}} & (4)\end{matrix}$

where μ is the dynamic viscosity of the fluid. If a traveling wavereaches a boundary at distance x in the conduit with a terminalimpedance Z_(T), defined by Equation 5:

$\begin{matrix}{{Z_{T}(x)} \equiv \frac{P\left( {x,t} \right)}{Q\left( {x,t} \right)}} & (5)\end{matrix}$

where P(x, t) and Q(x, t) are the local instantaneous transmuralpressure and volumetric flow rate, respectively, a fraction of the wavewill be reflected if Z_(T)≠Z_(o). The fraction of the wave reflected maybe embodied by the reflection coefficient Γ given by Equation 6:

$\begin{matrix}{\Gamma = \frac{Z_{o} - Z_{T}}{Z_{o} + Z_{T}}} & (6)\end{matrix}$

In short, for the systems and techniques described herein, Equations 1-6establish that: i) a local deviation in either the available area forflow, or the effective distensibility of the tubing, causes at least apartial reflection of elastic waves propagated through the tubing; andii) for tubing of uniform properties and cross-section, the outgoing andreflected elastic waves will transit the unaffected length of tubing ata common speed. Thus, if the transit time T of an elastic wave from thepressure sensor 151A, to the affected location (e.g., the location ofthe occlusion 1008), and back to the pressure sensor 151A is measured,and if the wave speed c_(o) is known, the distance x along the conduitfrom the location of the pressure sensor 151A to the location of theocclusion 1008 can be determined according to Equation 1.

Because the outgoing and reflected elastic waves will transit the lengthof the tube at a common speed in a given system (e.g., because thepropagation speed c_(o) is a function of the material properties of thetube, the dimensions of the tube, and the density of the fluid travelingthrough the tube), the propagation speed c_(o) may be initiallydetermined for a given system (e.g., the dialysis system 100). Once thepropagation speed c_(o) is known, the transit time T of elastic wavescan be measured. The distance x along the conduit from the location ofthe pressure sensor 151A to the location of the occlusion 1008 (e.g.,the location of the occlusion) can then be determined.

In some implementations (e.g., implementations in which the conduitincludes segments connected in series, such as a patient line and acatheter connected in series), the various segments of the conduit mayhave different elastic properties and/or cross-sectional dimensions.Further, the segments may be connected by fittings with yet other valuesof elastic properties and dimensions. While such complexities in thephysical conduit carrying elastic waves may cause complexities in thecharacteristic relationship of transit time T versus distance x to theocclusion, this relationship may still be repeatable and monotonic, thuspreserving the effectiveness of the method described herein.

Experiment 1

FIG. 11 shows an example experimental system 1100 in which thepropagation speed c_(o) of elastic waves can be determined. The system1100 includes a syringe pump 1110 that is configured to produce flowinto a conduit that includes a tube 1130 (e.g., which mimics a patientline) and a catheter 1102 connected to the tube 1130 via a port 1104. Inthis example, the syringe pump 1110 was driven by a programmable steppermotor. The catheter 1102 is submerged in a reservoir of fluid 1112(e.g., in place of a patient). An occlusion 1108 is present in the tube1130 at various distances x from a pressure sensor 306 that ispositioned at a proximal end of the tube 1130. In this example, theocclusion was created by hemostat clamping the tube 1130 at variousdistances x. The clamping of the tube 1130 represents a completeocclusion.

A small volume (e.g., approximately 0.32 cubic centimeters) of water wasinjected by the syringe pump 1110 at a fixed rate (e.g., a relativelyhigh rate of flow of 6.4 cubic centimeters per second). For example, thefixed rate of flow may create an impulse (e.g., a step input and/or anear-instantaneous pulse) in local pressure. At the end of thedispensing stroke, the flow of water was abruptly stopped. The tube 1130develops a local distension in cross-sectional area due to the suddeninjection of water that travels axially along the wall of the tube 1130as an elastic wave. The elastic wave carries with it local pressurevariations. As the elastic wave travels distally along the tube 1130, itreaches the occlusion 1108, and at least a portion is reflected backproximally toward the pump 1110.

The pressure sensor 1106 is configured to measure the pressure in thetube 1130 at the proximal end of the tube 1130 over time. The pressuremeasurements can be used to detect reflections of the elastic waves, inparticular, times at which such reflections arrive at the proximal endof the tube 1130. In some implementations, the pressure measurementsoccur at a frequency in the order of ones of hertz, tens of hertz (e.g.,1-99 Hz), hundreds of hertz, or thousands of hertz (e.g., 1 kHz -2 kHz).The experiment is repeated at various distances x of the occlusion 1108.

FIGS. 12A-G show representative graphs of pressure P (in mbar) measuredby the pressure sensor 1106 versus time (in seconds). The occlusions1108 (e.g., the clamping of the tube 1130) occur at distances x of 80cm, 100 cm, 140 cm, 180 cm, 220 cm, 260 cm, and 295 cm, respectively.

Referring to FIG. 12C, which shows pressures P measured when the tube1130 was clamped at a distance x of 140 cm, the measured pressure isinitially slightly above ambient and rises substantially uniformlyduring the pumping stroke. After the substantially uniform rise,oscillations occur. The period T of the oscillations (e.g., the transittime T of the elastic wave from the pressure sensor 1106, to thelocation of the occlusion 1108, and back to the pressure sensor 1106) isapproximately 78 milliseconds. Using Equation 1, the propagation speedc_(o) of the elastic waves is determined to be approximately 36 metersper second.

The calculation of the propagation speed c_(o) with reference to FIG.12C is made under the assumption that the oscillations are attributableto successive arrivals of a reflected elastic wave. Because thepropagation speed c_(o) should be uniform across various locations ofthe occlusion 1108 (e.g., in the case of uniform tubing), additionaltests were performed at various distances to corroborate the validity ofEquation 1 and confirm that the oscillations were attributable tosuccessive arrivals of a reflected elastic wave. While FIGS. 12A-G showrepresentative graphs of pressure versus time for clampings that werelocated at distances of 80 cm to 295 cm, pressures may be measured usingother clamping locations. In some implementations, additional signalprocessing can be performed to extend limits of occlusion detection toany location of occlusions.

FIG. 13 shows a representative graph of the periods T of theoscillations (in milliseconds) versus the various distances x of theclamping locations (in centimeters). The measured periods T are based onthe data shown in FIGS. 12A-G. The data shown in FIG. 13 indicates thatthe measured periods T (e.g., the transit time T of the elastic wavefrom the pressure sensor 1106, to the location of the occlusion 1108,and back to the pressure sensor 1106) are commensurate with thecorresponding clamping distances x. That is, the data verify that thepropagation speed c_(o) of the elastic waves is substantially uniform(e.g., approximately 36±2 m/s) for all of the distances x measured,thereby corroborating the validity of Equation 1 and confirming that theoscillations are attributable to successive arrivals of reflectedelastic waves. Now that the propagation speed c_(o) is known, thetransit time T of elastic waves can be measured to determine unknowndistances x of other occlusions 1108 which may occur.

In some examples, the empirical determination of oscillation period Tversus clamping distances x can be performed to characterize or“calibrate” the relationship between period T and distance x whileaccounting for non-uniform segments of the conduit. For example, theslope of the period T versus distance x curve of FIG. 13 may change atcertain junctions in the conduit assembly, which in some examples canhave the effects of enhancing the sensitivity of the detection method.In some examples, prior to treatment, an empirical determination can bemade in which an occlusion is intentionally applied at known distancesx, thereby providing a specific calibration of the current conduitassembly.

Experiment 2

While Experiment 1 corroborated the validity of Equation 1 in theexperimental system 1100 of FIG. 11 testing for complete occlusions,Experiment 2 studies a similar technique implemented in an actualdialysis machine (e.g., the PD machine 102 of FIGS. 1-10) using thebuilt-in pressure sensor 151A to test for partial occlusions. Theadvanced testing described below was performed to achieve results thatare more relevant to real PD treatment.

The experiment primarily focused on flow in the drain direction. Thechoice to focus on flow in the drain direction was made for thefollowing reasons: i) a majority of problematic blockages typicallyoccur in the drain direction; ii) a greater potential for difficulty waspredicted in the drain direction due to possible pull-off of cassettefilm from the pump; and iii) initial tests in the fill directionsuggested that the same patterns of pressure versus flow should beobtainable—albeit with the potential for different calibration curvesthat may need to be empirically determined.

FIG. 14 shows a schematic of a dialysis system 1400 in which thepropagation speed c_(o) of elastic waves can be determined. The dialysissystem 1400 includes the PD machine 102, the PD cassette 112 housed inthe PD machine 102, a patient line 1430, and the pressure sensor 151Alocated at a proximal end of the patient line 1430. The patient line1430 may be substantially similar to the patient line 130 describedabove with respect to FIGS. 1 and 10. In some implementations, thepatient line 1430 may be a 10foot patient line with dual patientconnectors. In this example, the PD machine 102 is controlled by acomputing device 1434 and a microcontroller 1436 such as an ATmega 2650microcontroller manufactured by Atmel Corporation. In someimplementations, the PD machine 102 may be controlled by a control unit(e.g., a processor) of the PD machine 102, such as the control unit 139shown in FIG. 1. The microcontroller 1436 is operatively coupled todriver modules 1438 a, 1438 b. The driver modules 1438 a, 1438 b may beDRV8825 stepper motor driver modules manufactured by Pololu Corporation.The dialysis system 1400 includes various experimental components thatcan perform the functions of: i) introducing a controlled level ofocclusion to the patient line 1430 at a known location; ii) enablingexternal programmable control of the pump heads to execute flowactuation according to the methods described herein; and iii) performingdata acquisition from the onboard pressure sensor (e.g., the pressuresensor 151A) and in some examples a separate inline pressure sensor forvalidation purposes.

The microcontroller 1436, at the direction of commands issued by thecomputing device 1434, is configured to control the driver modules 1438a, 1438 b to cause the driver modules 1438 a, 1438 b to operate pumps(e.g., the piston heads 134A, 134B) of the PD machine 102 in order toimpose specified flow patterns. The microcontroller 1436 and the drivermodules 1438 a, 1438 b provided pulse streams to the stepper motorsdriving the pumps to accomplish the following types of motion: i) returnto the “home” position as defined by an onboard limit switch; ii) moveforward at a specified step rate (e.g., to achieve a particular flowrate), by a specified number of steps, in a user-defined stepping modefrom full stepping to various increments of microstepping; and iii) movebackward at a specified step rate, by a specified number of steps in auser-defined stepping mode. Some flow patterns (e.g., characterized bycombinations of step rates, number of steps, stepping mode, etc.) weredetermined to be more desirable than others for the purpose of occlusiondetection. Such desirable flow patterns were programmed in a sequencethat is described below.

The pumps are configured to cause fluid to be pumped through a patientline-catheter conduit that includes the patient line 1430, a catheter1402, and a port 1404 that connects the patient line 1430 to thecatheter 1402. The catheter 1402 may be a Flex Neck Classic catheter.The catheter 1402, the port 1404, and a portion of the patient line 1430is submerged in a basin of water 1412 (e.g., in place of a patient). Thewater was held at room temperature (e.g., 20-25° C.). The free surfaceof the water was kept at the same height (e.g., ±1 centimeters) withrespect to the direction of gravity as that of the pressure sensor 151Aof the PD cycler 102. An occlusion 1408 was provided in the patient line1430 at various distances x from the pressure sensor 151A. In thisexample, the occlusion 1408 was created using various methods and atvarious distances x, as described in more detail below. The occlusions1408 represented both full and partial occlusions.

The experiment included the following general steps:

-   -   i. create an impulsive change in a pressure condition at the        proximal end of the patient line 1430 (e.g., at the location of        the pressure sensor 151A) by providing a short burst of water        flow in either the fill or the drain direction that is abruptly        ceased, thereby creating elastic waves in the patient line 1430;    -   ii. detect and measure the transit time T for elastic waves to        travel from the pressure sensor 151A, to the location of the        occlusion 1408, and back to the pressure sensor 151A; and    -   iii. empirically determine a calibration curve between the        transit time T and the distance to the occlusion x, thereby        determining an effective value of the propagation speed c_(o) of        the elastic waves.

The experiment was performed across a large number of cassettes, withdifferent types, degrees, and locations of flow restriction (e.g.,occlusions), in order to investigate the potential sensitivity (e.g.,true positive rate) and specificity (e.g., true negative rate) of thedetection method, as described in more detail below.

A small volume (e.g., approximately 0.33 cubic centimeters) of water wasmoved through the patient line 1430 in the drain direction by a firstpump of the PD machine 102 (e.g., a pump controlled by a first one ofthe driver modules 1438 a) at a fixed rate (e.g., 4.4 cubic centimetersper second). At the end of the stroke, the first pump was abruptlystopped. The patient line 1430 develops a local deformity due to theinjected water. Such a deformity causes elastic waves to be generated inthe patient line 1430. The pressure sensor 151A, which is built into thePD machine 102 and located at the proximal end of the patient line 1430,was used to detect the reflected elastic waves in a manner substantiallysimilar to that described above with respect to FIG. 11.

The partial occlusions 1408 used in the experiment were characterizedfor their relative flow restrictions. The characterization was donequantitatively via the fluidic resistance R_(f) values of the partialocclusions 1408 as given by Equation 7:

$\begin{matrix}{R_{f} = \frac{{\Delta \; P}}{Q}} & (7)\end{matrix}$

where

ΔP=pressure difference from upstream to downstream of occlusion   (8)

and

Q=volumetric flow rate   (9)

The pressures were initially measured using both the pressure sensor151A of the PD machine 102 and a reference pressure transducer 1440positioned downstream from the pressure sensor 151A. The separatepressure measurements were taken to ensure that the pressure sensor 151Abuilt into the PD machine 102 was capable of achieving the sensitivityrequired to detect the elastic waves. For example, the pressure sensor151A is configured to detect the pressure in the patient line 1430through a membrane of the cassette 112, and various fluidic elements arepositioned between the pressure sensor 151A and the proximal end of thepatient line 1430. It was considered that these elements may have thepotential to diminish and/or distort the elastic waves. Thus,measurements made by the reference pressure transducer 1440 were used toverify the fidelity of the measurements made by the pressure sensor151A. A high degree of fidelity was observed, and the reference pressuretransducer 1440 was removed to avoid possible artifacts.

Utilizing only measurements from the pressure sensor 151A of the PDmachine 102, ΔP due to the applied occlusion 1408 was inferred by firstobtaining a baseline pressure measurement with no occlusion 1408. Thebaseline pressure measurement was then subtracted from the pressuremeasurement with the occlusion 1408 according to Equation 10:

ΔP=Pwith occlusion−Pwithout occlusion   (10)

Due to the likelihood of turbulent flow and other sources of viscouspressure losses that are not linearly related to Q, the fluidicresistance R_(f) for a given flow restriction is in general a functionof Q. In order to isolate the effect of flow resistance from capacitiveor inertial effects, ΔP is measured at steady state. For these reasons,measurements related to the fluidic resistance R_(f) were performedunder prolonged flow at a fixed flow value (e.g., a fixed flow value ofQ=30 milliliters per minute). Such a flow value was chosen because itrepresents the critical value for the Drain Complication condition,described in more detail below, and is representative of the order ofmagnitude of mean flow rate occurring throughout a treatment.

The ability to detect a partial occlusion (e.g., as compared todetecting a complete occlusion) presents challenges that do not manifestwhen detecting a complete occlusion. Typically, the less restrictive anocclusion is, the greater is the challenge for sensitivity andspecificity of a method for determining its location. A relevantstandard for quantifying partial occlusions in the PD machine 102 comesfrom the Drain Complication and Fill Complication conditions. DrainComplication and Fill Complication conditions occur when there is a flowrestriction sufficient to depress the flow below a threshold value for aparticular period of time. In a model case of a steady-state flowrestriction, the threshold value of restriction that would generate aDrain Complication is one that would require a pressure of approximately−200 mbar (as measured at the pressure sensor 151A) to drive a flow ofapproximately 30 milliliters per minute. Thus, the measurements relatedto the fluidic resistance R_(f) were performed under prolonged flow atthe fixed flow rate of Q=30 milliliters per minute. An occlusion thatrequires −200 mbar to produce a steady-state flow rate of 30 ml/min isreferred to herein as a “drain-critical occlusion.”

Applying Equation 7 to the conditions defined by the “drain-criticalocclusion,” the total fluidic resistance of the system 1400 can bedetermined according to Equation 11:

$\begin{matrix}{R_{f}^{{{drain} - {critical}},{total}} = {\frac{200\mspace{14mu} {mbar}}{30\mspace{14mu} {ml}\text{/}\min} = {6.7\frac{mbar}{{ml}\text{/}\min}}}} & (11)\end{matrix}$

In Equation 11, the superscript “total” refers to the fact that thepressure sensor 151A shows the effect of all fluidic resistancesoccurring in, and inherent to, the cassette 112, the patient line 1430,and the catheter 1402. Thus, some components of the total fluidicresistance are due to normally occurring elements in the flowpath (e.g.,the conduit), R_(f) ^(baseline). Because such normally occurringelements are arranged in series with the additional resistance createdby the occlusion 608, and due to the additive property of resistances inseries, a drain-critical value of occlusion-specific resistance R_(f)^(drain-critical.occlusion) can be determined according to Equation 12:

Rd_(f) ^(drain-critical,occlusion)=R_(f) ^(drain-critical,total)−R_(f)^(normal)   (12)

R_(f) ^(baseline) for patient line 1430, the port 1404 with two patientconnectors, and the catheter 1402 was measured to be approximately 0.095mbar/(ml/min). Thus, the drain-critical value of the fluidic resistanceof a partial occlusion itself is approximately 6.7 mbar/(ml/min). Overthe course of Experiment 2, partial occlusions 1408 were tested withocclusion-specific resistances in the range of approximately 1-10mbar/(ml/min), thus representing values in the range of approximately0.15-1.5 times the drain-critical value of occlusion-specific resistanceR_(f) ^(drain-critical.occlusion).

The partial occlusions 1408 were designed to model two basic types ofreal occlusions: i) internal occlusions (e.g., in which an obstructionlodges itself within the lumen of the patient line 1430; and ii)external occlusions, in which the patient line 1430 is pinched from theoutside. In designing the physical means of applying the partialocclusions 1408 to the patient line 1430 and/or the catheter 1402, thegoal was to determine whether the detection method can provide ameasurement of the distance x of the occlusion 1408 that is sensitiveand specific for the distance x but insensitive to the type ofrestriction or the value of the fluidic resistance R_(f) of theocclusion 1408 (e.g., for fluidic resistance R_(f) values within therange of interest of approximately 1-10 mbar/(ml/min)).

Partial occlusions 608 of both types (e.g., internal and external)having repeatable fluidic resistance R_(f) values were applied atvarious locations x over a relatively large number of cases to test forrepeatability.

FIG. 15 shows a cross-sectional view of an example partial internalocclusion 1502 installed in the patient line 1430. The partial internalocclusion 1502 was fabricated to serve as a model of an internalocclusion. For example, the partial internal occlusion 1502 is meant torepresent a partially blocked patient line, with a well-controlledorifice of known flow characteristics. The partial occlusion 1408 ofFIG. 14 may represent the partial internal occlusion 1502. In thisexample, the internal occlusion 1502 is a cylindrical insert made ofstainless steel, although other shapes and/or materials may be used. Theinternal occlusion 1502 is configured to be positioned at a chosendistance x such that the internal occlusion 1502 is sufficiently grippedby the patient line 1430 in order to remain in position throughout thetests. The internal occlusion 1502 includes a circular orifice 1504 forallowing the fluid tested (e.g., water) to flow through the internalocclusion 1502. The orifice 1504 has a diameter that results in theinternal occlusion 1502 having a fluidic resistance R_(f) value in therange of 1-10 mbar/(ml/min). The diameter of the orifice 1504 may resultin particular fluidic resistance R_(f) values for the occlusion 1502according to Table 1:

Diameter of orifice R_(f) (mm) mbar/(ml/min) 0.30 8.7-9.1 0.34 5.5-6.40.38 3.1-3.2 0.51 0.8-1.0

The fluidic resistance R_(f) values of the occlusion 1502 as shown inTable 1 depend on the particular working fluid used in the system 1400(e.g., in this example, water). Thus, if a different fluid were used,such as dialysate, the fluidic resistance R_(f) values would bedifferent. The diameter or the orifice 1504 may be configured to have adiameter that results in appropriate fluidic resistance R_(f) valuesbased on the working fluid that is used. In this example, the diametersof the orifice 1504 were chosen to achieve the desired fluidicsimilarity with known conditions of interest for dialysate flow, usingthe drain-critical value R_(f) as a benchmark as discussed above. Thus,the results presented herein are largely sufficient to validate themethod for its applicability to the condition of dialysate as theworking fluid. However, at least two characteristics would be expectedto vary to some extent if dialysate were substituted for water as usedin these tests. For example, the exact value of the propagation speedc_(o) of the elastic waves is affected by the density of the fluidaccording to Equation 2. Further, the diameter of occlusion required toachieve a particular value of fluidic resistance is a function of fluidviscosity.

FIGS. 16A and 16B show a cutaway view and a photograph, respectively, ofan example partial external occlusion applied to the patient line 1430.The partial external occlusion was fabricated to serve as a model of anexternal “pinching” style of occlusion. For example, the partialexternal occlusion is meant to represent the style of occlusionoccurring when the patient line 1430 is pinched or kinked, with theapplied value of restriction being precisely controlled during the test.The partial occlusion 1408 of FIG. 14 may represent the partial externalocclusion 1502. In this example, the external occlusion is in the formof a clamping mechanism 1602 that is configured to apply a partialocclusion of the pinching type. The clamping mechanism 1602 includesrods 1604 that are configured to apply uniform stresses to substantiallyopposite surfaces of the patient line 1430 that cause the patient line1430 to deform. In this example, the rods 1604 are made of stainlesssteel and have a diameter of 3.2 millimeters, although other dimensionsand/or materials may be used. The stress applied to the patient line1430 may be referred to as a Hertzian line-contact stress. The clampingmechanism 1602 also includes washers (e.g., Belleville washers) that areconfigured to cause the rods 1604 to press together as the clampingmechanism 1602 is tightened. For example, an operator may tighten theclamping mechanism 1602 during a “long-stroke” (e.g., having a flowvalue of approximately 30 milliliters per minute) to achieve a targetpressure reading by the pressure sensor 151A, thereby actively settingthe fluidic resistance R_(f) value of the external occlusion desired forthe particular test.

Referring again to FIG. 14, prior to any sequence of tests concerning aparticular cassette 112, locations on the patient line 1430 weremeasured with a precision of approximately ±3 millimeters. The patientline 1430 and the catheter 1402 were then primed with water tosubstantially eliminate the presence of air bubbles in the conduit. Thepartial occlusion 1408 was then placed such that the occlusion 1408 wascentered at the desired distance x. The testing was repeated for partialocclusions 1408 of both the internal and external type and havingvarious fluidic resistance R_(f) values.

For partial occlusions 1408 of the internal type (e.g., such as thepartial internal occlusion 1502 of FIG. 15), the occlusion 1408 wasfirst positioned near a distal end of the patient line 1430 (e.g., at adistance of approximately x=295 centimeters). The occlusion 1408 wasthen repositioned to various distances x for subsequent tests. Similartests were also performed with the occlusion 1408 positioned in thecatheter 1402. The patient line 1430 was primed after each repositioningof the occlusion 1408 to minimize the occurrence of air bubbles. Forpartial occlusions 1408 of the external type (e.g., such as the partialexternal occlusion in the form of a clamping mechanism 1602 of FIGS. 16Aand 16B), the occlusion 1408 was positioned to the various distances xfor testing. The patient line 1430 was primed after each repositioningof the occlusion 1408 to minimize the occurrence of air bubbles.

With the occlusion 1408 in place, both a “long-stroke” test formeasuring the fluidic resistance R_(f) of the occlusion 1408 and a“short-stroke” test (e.g., a sudden injection of approximately 0.32cubic centimeters of fluid at a fixed flow rate of approximately 6.4cubic centimeters per second) for determining the location of theblockage (e.g., the distance x) were performed.

The long-stroke test included a single, prolonged motion of the pump ata constant speed corresponding to a flow rate of Q=30 milliliters perminute. As described above, the pump is operated by the microcontroller1436 and the driver modules 1438 a, 1438 b. The pressure sensor 151A wasmonitored during the test. The pressures measured by the pressure sensor151A typically approached a steady-state value from the mid- toend-point of the stroke. The steady-state value was recorded for thepurpose of calculating the fluidic resistance R_(f).

The short-stroke test included one or more single rapid motions of thepump that were designed to impart a pressure impulse on the patient line1430, thereby causing an elastic wave to be generated in the patientline 1430 as described above. The short-stroke test was performed bymoving water having a volume of approximately 0.33 cubic centimetersthrough the patient line 1430, although other volumes could be used tooptimize signal-to-noise ratio or the operational limitations of thedialysis system 1400. For a particular value of dispensed volume, thespeed of the pump was maximized under appropriate constraints in orderto maximize the amplitude of the pressure waveforms associated with thetransit of the elastic waves. The constraints included avoidance ofmissed motor steps (e.g., momentary stalling of the motor by requiringpower beyond its capability), avoidance of pressures outside the rangeof the pressure sensor 151A, and avoidance of damage to components ofthe dialysis system 1400.

Regarding avoidance of missed motor steps, preliminary tests wereconducted with full-stepping of the pump stepper motor with pulse delaysof 2.00, 2.50, and 3.00 milliseconds. Steps were occasionally missed forthe 2.00 and 2.50 millisecond pulse delays, but were not missed for the3.00 millisecond pulse delays. Thus, full-stepping of the pump motorwith a total pulse delay of 3.00 milliseconds for 25 steps was employed,which resulted in a dispensed volume of 0.33 cubic centimeters.Pressures outside the range of the pressure sensor 151A and damage tocomponents of the dialysis system 1400 were not observed to occur whenoperating at any of the pulse delays.

FIG. 17A shows a pressure waveform 1702 that includes pressuremeasurements over time made by the pressure sensor 151A during theshort-stroke test. The pressure measurements were sampled at a frequencyof 1 kHz. In this example, the occlusion 1408 was positioned at adistance x=220 centimeters along the patient line 1430. The pump strokehad a duration of approximately 75 milliseconds. The measured pressure,steady in the absence of pump motion, is seen to drop rapidly during apump stroke having a duration of approximately 75 milliseconds thatcommences at approximately t=1 second. After abrupt cessation of pumpmotion, oscillations occur due to the elastic effects described above.The period T of the oscillations (e.g., which corresponds to the transittime T of the elastic waves from the pressure sensor 151A, to thelocation of the occlusion 1408, and back to the pressure sensor 151A)can be evaluated to determine the propagation speed c_(o) of the elasticwaves according to Equation 1. Once the propagation speed c_(o) of theelastic waves is known, locations x of occlusions (e.g., at unknownpositions of the conduit) can subsequently be determined by evaluatingthe period T of oscillations.

Superimposed with the oscillations is high-frequency noise and a gradualdecay from the peak excursion of pressure (e.g., at approximatelyt=1.075 seconds) toward zero. The decay occurs due to the occlusion 1408being a partial occlusion. Because the high-frequency noise and thedecay are not relevant for purposes of determining the period T of theoscillations, they can be removed from the waveform 1702 using one ormore signal processing techniques. For example, the waveform 1702 can besmoothed to reduce the effect of the high-frequency noise using a movingaverage taken as the mean of the measured pressures spanning 15milliseconds on either side of a given data point (e.g., sometimesreferred to as a 15 millisecond half-width moving average). Further, abackground curve approximating the overall decay onto which theoscillations are superimposed can be subtracted from the waveform 1702.The background curve to be subtracted from the waveform 1702 may beobtained, for example, using a 50 millisecond half-width moving average.Prior to applying the moving averages, the data were truncated to thetime domain which begins at the cessation of the pump motion atapproximately t=1.075 seconds.

FIG. 17B shows a pressure waveform 1704 that includes the data of FIG.17A after being smoothed and after having the background curvesubtracted. The waveform 904 has a relatively more symmetrical patternas compared to the waveform 1702 of FIG. 17A, thereby enabling a moreaccurate evaluation of the oscillation period T.

The data shown in FIGS. 17A and 17B correspond to the short-stroke testperformed with a dispensed water volume of 0.33 cubic centimeters at afixed rate of 4.4 milliliters per second for an occlusion 1408positioned at a distance x=220 centimeters along the patient line 1430.Data was also obtained for various other cassette 112/occlusion 1408configurations at various different distances x for the occlusion 1408.For example, 15 different cassette-occlusion combinations were used, forboth internal and external partial occlusions, and each combination wastested at 5-8 different distances x for the occlusion 1408. For eachtest, the period T of the resulting oscillations was evaluated using atleast three different methods: i) first half-wave period; ii) otherhalf-and full-wave periods; and iii) Fast Fourier Transform. It wasdetermined that the first half-wave period method achieved the greatestsensitivity and specificity for determining the distance x of theocclusion 1408.

Sensitivity and specificity are statistical measures of the performanceof the detection method. The sensitivity, also referred to as the truepositive rate, measures the proportion of positives that are correctlyidentified as such. In this context, the sensitivity may correspond tothe ability of the system to correctly identify occlusions (e.g., fordistances x within a particular range). The specificity, also referredto as the true negative rate, measures the proportion of negatives thatare correctly identified as such. In this context, the specificity maycorrespond to the accuracy of the detection method (e.g., the margin oferror of determined distances x).

The first half-wave period is the time measurement from the end of thepump motion to a first local extremum of the pressure measurements,represented by T₁ in FIG. 17B. For drain-direction flow, the first localextremum is a local maximum. As compared to latter half-waves (e.g., T₂and T₃), sensitivity and specificity benefit from certain features ofthe first half-wave. For example, onset is relatively precise because itis well defined by the cessation of the pump motion (e.g., duringshort-stroke testing), the timing of which can be measurable with highprecision. Further, completion of the first half-wave can be measuredwith a relatively high signal-to-noise ratio due to the signalmaximization and the noise minimization associated with the firsthalf-wave period. For example, the first half-wave presents the elasticwave with its maximum amplitude, which maximizes the precision ofmeasuring the extremum that defines its endpoint by minimizing theeffect of various sources of noise on the measurement. After the firsthalf-wave, a rapid decay of amplitude in the subsequent oscillationsoccurs due to viscoelastic effects and the effects of partial wavereflection (e.g., as described above with reference to Equation 6).Further, subsequent wave reflections may generate additional sources ofnoise due to constructive and destructive interference of partiallytransmitted waves. The effects of such noise do not manifest in thefirst half-wave period.

The latter half-wave periods (e.g., the second half-wave period T₂ andthe third half-wave period T₃) appear to have substantially equaldurations (e.g., as might be expected of a naturally resonating wave),while the first half-wave period T₁ appears to be relatively shorter(e.g., because the first half-wave period T₁ is the incipient periodupon impulsively starting the elastic wave). Thus, it was not obvious apriori that the half-wave period T₁ would correlate well with thedistance x of the occlusion 1408. However, use of the first half-waveproduced the best sensitivity and specificity in the analyses performed.

As the name implies, because the first half-wave period T₁ onlyrepresents half of the period T of the oscillations, the first half-waveperiod T₁ corresponds to the transit time of the elastic wave from thepressure sensor 151A to the location of the occlusion 1408 (e.g., notthe full round-trip transit time T). Thus, when using the firsthalf-wave period T₁ to determine the distance x to the occlusion 1408,Equation 1 can be simplified as Equation 13:

X=T ₁ *c _(o)   (13)

where T₁ is the first half-wave period, c_(o) is the propagation speedof the elastic waves, and x is the distance along the conduit from thelocation of the pressure sensor 151A to the location of the occlusion1408.

FIG. 18 shows a representative graph of the first half-wave periods ofthe oscillations (in seconds) versus the various distances x of theocclusions 1408 (in centimeters) for the 15 different cassette-occlusioncombinations. The occlusions 1408, of both the internal and externaltypes, were located at various distances x that correspond to positionsalong the patient line 1430 (e.g., x=60, 100, 140, 150, 180, 200, 220,250 centimeters), distances x that correspond to positions between thepatient connectors of the port 1404 (e.g., x=304-307 centimeters), anddistances that correspond to positions along the catheter 1402 (e.g.,x=310-365 centimeters). The occlusions 1408 had various fluidicresistance R_(f) values (e.g., R_(f)=5.9-6.4, 8.7-9.1, 5.5-5.9, 3.1-3.2,0.8-1.0, 6.4-10.2, 7.0-9.6, 5.2-7.0, 1.4-2.2, 8.0-8.5, 6.3-6.9, 1.3-1.8,8.2-9.6, 6.6-7.8, and 1.5-2.1 mbar/(ml/min)).

Among the distances x tested, evaluation of the first half-wave periodresulted in sensitivity (e.g., the ability to correctly identifyocclusions) for distances x greater than or equal to approximately 100centimeters. In some examples, for distances x of less than 100centimeters, the local maxima of the pressure measurements may beundetectable. The range of sensitivity may be extended to lower distancevalues x by increasing the strength of the pressure impulse and/or byimplementing additional or alternate signal processing of the pressurewaveforms (e.g., 1702, 1704 of FIGS. 17A and 17B).

Recalling that the goal of this experiment was to determine whether thedetection method can provide a measurement of the distance x of theocclusion 1408 that is sensitive and specific for the distance x butinsensitive to the type of restriction or the value of the fluidicresistance R_(f) of the occlusion 1408, the first half-wave periodscorresponding to each distance x would ideally be identical. However,the vertical scatter seen in the data of FIG. 18 implies a specificity(e.g., an accuracy) of approximately ±40 centimeters. In someimplementations, the detection method may be employed to determine inwhich of five sections/zones the occlusion 1408 is located. For example,the detection method can be used to determine whether the occlusion 1408is located in a first zone of the patient line 1430 (e.g., approximatelyx=0-100 centimeters), in a second zone of the patient line 1430 (e.g.,approximately x=100-200 centimeters), in a third zone of the patientline 1430 (e.g., approximately x=200-295 centimeters), between thepatient connectors of the port 1404 (e.g., approximately x=304-307centimeters), or in the catheter 1402 (e.g., approximately x=310-365centimeters).

While the detection method described above largely focuses on using thefirst half-wave period for evaluating the period T of the oscillations,other methods can be employed. For example, the second half-wave periodor the third half-wave period (e.g., T₂ and T₃, respectively, as shownin FIG. 17B) can be evaluated. Alternatively, frequency-based signalanalyses (e.g., Fast Fourier Transform) may be used to determine thedistance to the occlusion x.

FIG. 19 shows a representative graph of the second half-wave periods ofthe oscillation (in seconds) versus the various distances x of theocclusions 1408 (in centimeters) for the 15 different cassette-occlusioncombinations, and FIG. 20 shows a representative graph of the thirdhalf-wave periods of the oscillation (in seconds) versus the variousdistances x of the occlusions 1408 (in centimeters) for the 15 differentcassette-occlusion combinations. Both graphs show a larger degree ofvertical scatter as compared to the vertical scatter present in the dataof FIG. 18, and thus indicate reduced specificity, for the reasonsdiscussed above with respect to FIG. 17B.

In some implementations, the Fast Fourier Transform (FFT) of thepressure waveform can be used to evaluate the period T of theoscillations. For example, the pressure waveform (e.g., 1702, 1704 ofFIGS. 17A and 17B) can be transformed into the frequency domain, and thetransform can be evaluated to determine the period T of theoscillations. However, a limited number of wave periods transpiringprior to the substantially full decay of the wave amplitude may resultin imprecision in the frequency space (e.g., due to the relatively shortwindow in the time domain), thereby resulting in diminished sensitivityand/or specificity.

In some implementations, the specificity is improved (e.g., the verticalscatter of the data is reduced) by employing additional signalprocessing to enhance the accuracy of the wave period measurement. Insome implementations, the specificity is improved by performing apre-test calibration routine to account for any cassette- or medicaltube/patient line-specific variations in the wave period versus thedistance x.

In some implementations, the specificity of the detection method isimproved by performing multiple short-stroke tests and averaging theresults. For example, referring to FIG. 21, a long-stroke test may beinitially performed (e.g., in the drain direction) during a first phase2102 in which the pump moves at a constant speed corresponding to a flowrate of Q=30 milliliters per minute. During the first phase 2102, thepump is withdrawn and fluid is pulled from the patient line 1430 intothe pump cylinder. The long-stroke test may be initially performed toadjust the configuration of a partial external occlusion (e.g., as shownin FIG. 16) in order to achieve the desired fluidic resistance beforeperforming the series of short-stroke tests. The initial mean pressurevalue may be subtracted from the pressure measurements. The steady-statepressure is used for determining the fluidic resistance R_(f) of thetotal flowpath. If the fluidic resistance R_(f) exceeds a thresholdvalue (e.g., a predetermined threshold value), multiple short-stroketests are performed to determine the location of the occlusion. During asecond phase 2104, the pump may be returned to position for the start ofthe short-stroke tests; however, in some implementations, the pump isnot returned to position (e.g., to avoid reversal of flow duringdetection). The second phase 2104 begins with a pause to allowtransients to complete, followed by a long pump-stroke in the filldirection (e.g., fluid is pumped from the pump cylinder into the patientline 1430). During a third phase 2106, the multiple short-stroke testsare then performed. The resulting pressure measurements, as well as anyanalyses performed to determine the location of the occlusion x, can beaveraged to reduce the uncertainty, thereby improving the specificity ofthe detection method.

While the detection method has been largely described as beingimplemented in a testing environment, similar techniques can be employedfor detecting occlusions in the conduit when the patient line isattached to a patient receiving a dialysis treatment (e.g., as shown inFIG. 10). For example, the detection method can be employed fordetermining the distance x of the occlusion 1008 in the conduit bymeasuring the period T of elastic wave oscillations generated in thepatient line 130 itself In particular, the propagation speed c_(o) ofthe elastic waves generated in a particular system configuration can bedetermined according to Equation 1 in advance of a treatment bypositioning a test occlusion at a known distance x and measuring theperiod T of the oscillations—that is, each specific cassette-patientline-port-catheter combination may be “calibrated” prior to use. Oncethe propagation speed c_(o) for the system is known, the period T ofoscillations can be measured during an actual dialysis treatment, andEquation 1 can be used to determine the distance x of the occlusion1008. Alternatively, an experimentally determined correlation betweenthe period T and the distance x of the occlusion 1008 may be used. Thetype of the occlusion 1008 can then be inferred based on the determinedlocation of the occlusion 1008, as described above.

While the dialysis system has been largely described as being aperitoneal dialysis (PD) system, other medical treatment systems canemploy the techniques described herein. Examples of other medicaltreatment systems include hemodialysis systems, hemofiltration systems,hemodiafiltration systems, apheresis systems, and cardiopulmonary bypasssystems.

FIG. 22 is a block diagram of an example computer system 2200. Forexample, the control unit (139 of FIG. 1), the computing device (1434 ofFIG. 14), and/or the microcontroller (1436 of FIG. 14) could be examplesof the system 2200 described here. The system 2200 includes a processor2210, a memory 2220, a storage device 2230, and an input/output device2240. Each of the components 2210, 2220, 2230, and 2240 can beinterconnected, for example, using a system bus 2250. The processor 2210is capable of processing instructions for execution within the system2200. The processor 2210 can be a single-threaded processor, amulti-threaded processor, or a quantum computer. The processor 2210 iscapable of processing instructions stored in the memory 2220 or on thestorage device 2230. The processor 2210 may execute operations such ascausing the dialysis system to carry out dialysis functions.

The memory 2220 stores information within the system 2200. In someimplementations, the memory 2220 is a computer-readable medium. Thememory 2220 can, for example, be a volatile memory unit or anon-volatile memory unit. In some implementations, the memory 2220stores information (e.g., executable code) for causing the pumps of thedialysis system to operate as described herein.

The storage device 2230 is capable of providing mass storage for thesystem 2200. In some implementations, the storage device 2230 is anon-transitory computer-readable medium. The storage device 2230 caninclude, for example, a hard disk device, an optical disk device, asolid-date drive, a flash drive, magnetic tape, or some other largecapacity storage device. The storage device 2230 may alternatively be acloud storage device, e.g., a logical storage device including multiplephysical storage devices distributed on a network and accessed using anetwork.

The input/output device 2240 provides input/output operations for thesystem 2200. In some implementations, the input/output device 2240includes one or more of network interface devices (e.g., an Ethernetcard), a serial communication device (e.g., an RS-232 port), and/or awireless interface device (e.g., an 802.11 card, a 3G wireless modem, ora 4G wireless modem). In some implementations, the input/output device2240 may include short-range wireless transmission and receivingcomponents, such as Wi-Fi, Bluetooth, and/or near field communication(NFC) components, among others. In some implementations, theinput/output device includes driver devices configured to receive inputdata and send output data to other input/output devices, e.g., keyboard,printer and display devices (such as the touch screen display 118). Insome implementations, mobile computing devices, mobile communicationdevices, and other devices are used.

In some implementations, the system 2200 is a microcontroller (e.g., themicrocontroller 1436 of FIG. 14). A microcontroller is a device thatcontains multiple elements of a computer system in a single electronicspackage. For example, the single electronics package could contain theprocessor 2210, the memory 2220, the storage device 2230, andinput/output devices 2240.

Although an example processing system has been described in FIG. 22,implementations of the subject matter and the functional operationsdescribed above can be implemented in other types of digital electroniccircuitry, or in computer software, firmware, or hardware, including thestructures disclosed in this specification and their structuralequivalents, or in combinations of one or more of them. Implementationsof the subject matter described in this specification can be implementedas one or more computer program products, i.e., one or more modules ofcomputer program instructions encoded on a tangible program carrier, forexample a computer-readable medium, for execution by, or to control theoperation of, a processing system. The computer readable medium can be amachine readable storage device, a machine readable storage substrate, amemory device, a composition of matter effecting a machine readablepropagated signal, or a combination of one or more of them.

The term “computer system” may encompass all apparatus, devices, andmachines for processing data, including by way of example a programmableprocessor, a computer, or multiple processors or computers. A processingsystem can include, in addition to hardware, code that creates anexecution environment for the computer program in question, e.g., codethat constitutes processor firmware, a protocol stack, a databasemanagement system, an operating system, or a combination of one or moreof them.

A computer program (also known as a program, software, softwareapplication, script, executable logic, or code) can be written in anyform of programming language, including compiled or interpretedlanguages, or declarative or procedural languages, and it can bedeployed in any form, including as a standalone program or as a module,component, subroutine, or other unit suitable for use in a computingenvironment. A computer program does not necessarily correspond to afile in a file system. A program can be stored in a portion of a filethat holds other programs or data (e.g., one or more scripts stored in amarkup language document), in a single file dedicated to the program inquestion, or in multiple coordinated files (e.g., files that store oneor more modules, sub programs, or portions of code). A computer programcan be deployed to be executed on one computer or on multiple computersthat are located at one site or distributed across multiple sites andinterconnected by a communication network.

Computer readable media suitable for storing computer programinstructions and data include all forms of non-volatile or volatilememory, media and memory devices, including by way of examplesemiconductor memory devices, e.g., EPROM, EEPROM, and flash memorydevices; magnetic disks, e.g., internal hard disks or removable disks ormagnetic tapes; magneto optical disks; and CD-ROM and DVD-ROM disks. Theprocessor and the memory can be supplemented by, or incorporated in,special purpose logic circuitry. The components of the system can beinterconnected by any form or medium of digital data communication,e.g., a communication network. Examples of communication networksinclude a local area network (“LAN”) and a wide area network (“WAN”),e.g., the Internet.

A number of implementations of the invention have been described.Nevertheless, it will be understood that various modifications may bemade without departing from the spirit and scope of the invention.Accordingly, other implementations are within the scope of the followingclaims.

What is claimed is:
 1. A method comprising: measuring a first pressureat a proximal end of a medical tube connected to a medical device;measuring a second pressure at the proximal end of the medical tube;determining an elapsed time between the first pressure measurement andthe second pressure measurement; and determining a location of anocclusion in the medical tube based on the elapsed time.
 2. The methodof claim 1, wherein the medical device comprises a dialysis machine. 3.The method of claim 2, wherein the dialysis machine comprises aperitoneal dialysis (PD) machine.
 4. The method of claim 1, wherein atleast one of the first pressure and the second pressure comprises alocal extremum of pressure measurements at the proximal end of themedical tube.
 5. The method of claim 4, wherein the local extremumcomprises at least one of a local maximum and a local minimum.
 6. Themethod of claim 1, wherein the first pressure and the second pressureare measured by a pressure sensor mounted at the proximal end of themedical tube.
 7. The method of claim 1, wherein the elapsed timerepresents a period of oscillations of an elastic wave.
 8. The method ofclaim 7, wherein the elastic wave originates from the proximal end ofthe medical tube.
 9. The method of claim 7, wherein the elastic wave isgenerated in response to at least one of an increase and a decrease inpressure in the medical tube.
 10. The method of claim 7, wherein a fluidflowing through the medical tube is at least partially blocked by theocclusion.
 11. The method of claim 10, wherein the fluid being at leastpartially blocked by the occlusion causes an increase or a decrease inpressure in the medical tube.
 12. The method of claim 9, wherein the atleast one of an increase and a decrease in pressure is in response to amotion of a pump of the medical device.
 13. The method of claim 7,wherein the oscillations of the elastic wave are caused at least in partby the elastic wave being reflected back from the location of theocclusion.
 14. The method of claim 1, wherein the medical tube comprisesa catheter at a distal end of the medical tube.
 15. The method of claim1, comprising inferring a type of the occlusion based at least in parton the determined location of the occlusion.
 16. The method of claim 15,wherein the type of the occlusion comprises one or more of a pinch ofthe medical tube, a kink in the medical tube, a deposit in the medicaltube, and a deposit blocking a hole of a catheter at a distal end of themedical tube.
 17. The method of claim 16, wherein the deposit comprisesomental fat.
 18. The method of claim 7, comprising determining thelocation of the occlusion in the medical tube based on the elapsed timeand a wave speed of the elastic wave.
 19. The method of claim 18,wherein the wave speed of the elastic wave is based on one or more ofdimensions of the medical tube, a material composition of the medicaltube, and a density of a fluid flowing through the medical tube.
 20. Themethod of claim 18, wherein the wave speed of the elastic wave isempirically determined.
 21. The method of claim 1, comprising performinga calibration prior to determining the location of the occlusion, thecalibration for determining a wave speed of an elastic wave propagatingthrough the medical tube.
 22. The method of claim 21, wherein thecalibration is for determining the wave speed of the elastic wavepropagating through the medical tube for a particular medical tube andcassette configuration used in the medical device.
 23. A methodcomprising: measuring a plurality of pressures at a proximal end of amedical tube connected to a medical device; determining one or moreelapsed times between local extrema of the measured pressures; anddetermining a location of an occlusion in the medical tube based on theone or more elapsed times.
 24. The method of claim 23, wherein the localextrema comprise at least one of a local maximum and a local minimum.25. The method of claim 23, comprising removing noise components fromthe measured pressures before determining the local extrema of themeasured pressures.
 26. The method of claim 23, wherein magnitudes ofthe pressure measurements decay over time when the occlusion is apartial occlusion.
 27. The method of claim 26, comprising subtracting,from the measured pressures, values that approximate the decay of thepressure measurements as a result of the occlusion being a partialocclusion before determining the local extrema.
 28. The method of claim23, wherein at least one of the local extrema of the measured pressurescorresponds to an end of a pump motion that causes fluid to flow throughthe medical tube.
 29. The method of claim 28, comprising determining anelapsed time between i) the end of the pump motion, and ii) anoccurrence of a local extrema that occurs after the end of the pumpmotion; and determining the location of the occlusion based on theelapsed time.
 30. The method of claim 29, wherein the elapsed timerepresents a first half-wave period of oscillations of an elastic wavegenerated in response to at least one of an increase and a decrease inpressure in the medical tube.
 31. The method of claim 23, comprisingperforming one or more signal processing techniques on the measuredpressures.
 32. A method comprising: measuring a first pressure at aproximal end of a medical tube connected to a medical device, themedical tube comprising a plurality of zones; measuring a secondpressure at the proximal end of the medical tube; determining an elapsedtime between the first pressure measurement and the second pressuremeasurement; and determining in which of the plurality of zones anocclusion is located based on the elapsed time.
 33. The method of claim32, wherein the medical tube comprises five zones.
 34. The method ofclaim 32, wherein the medical tube comprises a catheter at a distal endof the medical tube, and at least one of the zones comprises thecatheter.
 35. The method of claim 34, wherein the medical tube comprisesa port connecting the catheter to the medical tube, and at least one ofthe zones comprises the port.
 36. A medical device comprising: a medicaltube having a proximal end connected to an outlet of the medical device;a pressure sensor mounted at the proximal end of the medical tube, thepressure sensor configured for measuring a first and second pressure atthe proximal end of the medical tube; and a processor configured fordetermining an elapsed time between the first pressure measurement andthe second pressure measurement, and determining a location of anocclusion in the medical tube based on the elapsed time.
 37. The medicaldevice of claim 36, wherein the medical device comprises a dialysismachine.
 38. The medical device of claim 37, wherein the medical devicecomprises a peritoneal dialysis machine.